NAME

       UR::Object::Property - Class representing metadata about a class property

SYNOPSIS

         my $prop = UR::Object::Property->get(class_name => 'Some::Class', property_name => 'foo');

         my $class_meta = Some::Class->__meta__;
         my $prop2 = $class_meta->property_meta_for_name('foo');

         # Print out the meta-property name and its value of $prop2
         print map { " $_ : ".$prop2->$_ }
               qw(class_name property_name data_type default_value);

DESCRIPTION

       Instances of this class represent properties of classes.  For every item mentioned in the
       'has' or 'id_by' section of a class definition become Property objects.

INHERITANCE

       UR::Object::Property is a subclass of UR::Object

PROPERTY TYPES

       For this class definition:
         class Some::Class {
             has => [
                 other_id => { is => 'Text' },
                 other    => { is => 'Some::Other', id_by => 'foo_id' },
                 bar      => { via => 'other', to => 'bar' },
                 foos     => { is => 'Some::Foo', reverse_as => 'some', is_many => 1 },
                 uc_other_id => { calculate_from => 'other_id',
                                  calculate_perl => 'uc($other_id)' },
             ],
         };

       Properties generally fall in to one of these categories:

       regular property
           A regular property of a class holds a single scalar.  In this case, 'other_id' is a
           regular property.

       object accessor
           An object accessor property returns objects of some class.  The properties of this
           class must link in some way with all the ID properties of the remote class (the 'is'
           declaration).  'other' is an object accessor property.  This is how one-to-one
           relationships are implemented.

       via property
           When a class has some object accessor property, and it is helpful for an object to
           assumme the value of the remote class's properties, you can set up a 'via' property.
           In the example above, an object of this class gets the value of its 'bar' property via
           the 'other' object it's linked to, from that object's 'bar' property.

       reverse as or is many property
           This is how one-to-many relationships are implemented.  In this case, the Some::Foo
           class must have an object accessor property called 'some', and the 'foos' property
           will return a list of all the Some::Foo objects where their 'some' property would have
           returned that object.

       calculated property
           A calculated property doesn't store its data directly in the object, but when its
           accessor is called, the calculation code is executed.

PROPERTIES

       Each property has a method of the same name

   Direct Properties
       class_name => Text
           The name of the class this Property is attached to

       property_name => Text
           The name of the property.  The pair of class_name and property name are the ID
           properties of UR::Object::Property

       column_name => Text
           If the class is backed by a database table, then the column this property's data comes
           from is stored here

       data_type => Text
           The type of data stored in this property.  Corresponds to the 'is' part of a class's
           property definition.

       data_length => Number
           The maximum size of data stored in this property

       default_value
           For is_optional properties, the default value given when an object is created and this
           property is not assigned a value.

       valid_values => ARRAY
           A listref of enumerated values this property may be set to

       doc => Text
           A place for documentation about this property

       is_id => Boolean
           Indicates whether this is an ID property of the class

       is_optional => Boolean
           Indicates whether this is property may have the value undef when the object is created

       is_transient => Boolean
           Indicates whether this is property is transient?

       is_constant => Boolean
           Indicates whether this property can be changed after the object is created.

       is_mutable => Boolean
           Indicates this property can be changed via its accessor.  Properties cannot be both
           constant and mutable

       is_volatile => Boolean
           Indicates this property can be changed by a mechanism other than its normal accessor
           method.  Signals are not emmitted even when it does change via its normal accessor
           method.

       is_classwide => Boolean
           Indicates this property's storage is shared among all instances of the class.  When
           the value is changed for one instance, that change is effective for all instances.

       is_delegated => Boolean
           Indicates that the value for this property is not stored in the object directly, but
           is delegated to another object or class.

       is_calculated => Boolean
           Indicates that the value for this property is not a part of the object'd data
           directly, but is calculated in some way.

       is_transactional => Boolean
           Indicates the changes to the value of this property is tracked by a Context's
           transaction and can be rolled back if necessary.

       is_abstract => Boolean
           Indicates this property exists in a base class, but must be overridden in a derived
           class.

       is_concrete => Boolean
           Antonym for is_abstract.  Properties cannot be both is_abstract and is_concrete,

       is_final => Boolean
           Indicates this property cannot be overridden in a derived class.

       is_deprecated => Boolean
           Indicates this property's use is deprecated.  It has no effect in the use of the
           property in any way, but is useful in documentation.

       implied_by => Text
           If this property is created as a result of another property's existence, implied_by is
           the name of that other property.  This can happen in the case where an object accessor
           property is defined

             has => [
                 foo => { is => 'Some::Other', id_by => 'foo_id' },
             ],

           Here, the 'foo' property requires another property called 'foo_id', which is not
           explicitly declared.  In this case, the Property named foo_id will have its implied_by
           set to 'foo'.

       id_by => ARRAY
           In the case of an object accessor property, this is the list of properties in this
           class that link to the ID properties in the remote class.

       reverse_as => Text
           Defines the linking property name in the remote class in the case of an is_many
           relationship

       via => Text
           For a via-type property, indicates which object accessor to go through.

       to => Text
           For a via-type property, indicates the property name in the remote class to get its
           value from.  The default value is the same as property_name

       where => ARRAY
           Supplies additional filters for indirect properies.  For example:

             foos => { is => 'Some::Foo', reverse_as => 'some', is_many => 1 },
             blue_foos => { via => 'foos', where => [ color => 'blue' ] },

           Would create a property 'blue_foos' which returns only the related Some::Foo objects
           that have 'blue' color.

       calculate_from => ARRAY
           For calculated properties, this is a list of other property names the calculation is
           based on

       calculate_perl => Text
           For calculated properties, a string containing Perl code.  Any properties mentioned in
           calculate_from will exist in the code's scope at run time as scalars of the same name.

       class_meta => UR::Object::Type
           Returns the class metaobject of the class this property belongs to

METHODS

       via_property_meta
           For via/to delegated properties, return the property meta in the same class this
           property delegates through

       to_property_meta
           For via/to delegated properties, return the property meta on the foreign class that
           this property delegates to

SEE ALSO

       UR::Object::Type, UR::Object::Type::Initializer, UR::Object